Water sources, such as river water, contain minute amounts of bromide ions, and when ozone treatment (water purification treatment to high standards) is performed, the bromide ions in the water react with ozone, and a reaction such as shown in FIG. 1 occurs, thereby generating bromate ions.
Bromate ions are considered to be carcinogenic and having genotoxicity, the WHO (World Health Organization) has set guideline values for the concentration thereof in drinking water at 0.01 mg/L, and in Japan as well, as of May 30, 2003, an amendment by ministry order was effected that sets the water quality standard value at 0.01 mg/L.
An analytical method generally used for analyzing bromate ions is the ion chromatograph post-column absorption intensity method. This analytical method is one in which bromate ions in a water sample are separated using a cation exchange column, sulfuric acid and an admixture of sodium nitrate and potassium bromide being added to the solution to convert the bromate ions into tribromine ions, and the tribromine ion method being used to measure the ultraviolet region absorption so as to perform quantitative determination. After the bromate ions are separated using chromatographic separation, the post column derivitization method by means of the tribromine ion method is used to measure the level of absorption of the 268 nm ultraviolet line.
In the ion chromatograph post-column (IC-PC) method, a two-stage reaction occurs: in the first reaction stage, bromate is converted by a potassium bromide/sulfuric acid solution to tribromine ions, and then in the second reaction, a sodium bromide solution is used to establish the linearity of the calibration line in the low-concentration region.BrO3−+5Br−+6H+→3Br2+3H2OBr2+Br−+Br3−
In the past, the color comparison method, the absorption intensity method, the gas chromatography method, and the ion chromatography method and the like have been used as methods for measuring bromate ions. With these methods, however, there were problems regarding sensitivity and interference by coexisting components, and it was difficult to make reliable determinations of bromate ions not exceeding 0.01 mg/L. In contrast, in Patent Reference 1, there is language describing art by which a reducing agent is added to a reagent, the reagent to which the reducing agent was added being used to determine minute quantities of ions in the liquid under measurement. Also, in Non-Patent Reference 1, there is language describing an absorption intensity method that uses a 1-cm cell, and in Non-Patent Reference 2, there is language describing an absorption intensity method that uses a 10-cm cell.
With the methods of measuring bromate ions of the past, there were problems of a complex apparatus configuration and the need for a large amount of time for the derivitization to tribromine ions.
Given the above, the present invention has as an object to provide a method and an apparatus for bromate ion measurement that can more quickly and simply perform and obtain higher-sensitivity measurement results than with conventional bromate ion measurement methods.